In general, in an alpine area, bad weather, such as sudden heavy rain, heavy snow or a thick fog, may occur unexpectedly due to a drastic change in temperature, unlike in a low-elevation area. When a person who does not have basic knowledge about an alpine area is located in an alpine area at night, he or she has the possibility of experiencing an accident due to sudden bad weather. In an alpine area, a suddenly frozen road may be a cause of a traffic accident. Accordingly, it is necessary to understand a change in temperature attributable to an increase in elevation in an alpine area with respect to each period of a year.
Automatic meteorological observation devices capable of collecting temperature data are intensively distributed in a populated area and are rare in a mountainous area, and have been used for short-term observation over the course of 1 to 2 years because the automatic meteorological observation devices may be easily damaged by wind, heavy rain and heavy snow prominent in an alpine area and also it is not easy to supply power to the automatic meteorological observation devices.
Accordingly, a method of estimating the temperature of a mountainous area from an infrared image has been developed. This is a method of converting the radiant energy of a land surface, collected via an infrared sensor, into temperature, and is advantageous in that the method can observe a wide area, can perform periodic monitoring, can reduce data acquisition costs, and can estimate land surface temperature lapse rate.
Technologies related to the calculation and estimation of land surface temperature are disclosed in Korean Patent No. 1207925 and Korean Patent Application Publication No. 2009-0088131.
A method of calculating land surface temperature and a method and system for estimating a local air temperature taking account of an elevation difference, which are disclosed in Korean Patent No. 1207925 and Korean Patent Application Publication No. 2009-0088131 as related technologies, respectively, are briefly described below.
According to Korean Patent No. 1207925 (hereinafter referred to as “related document 1”), the method of calculating land surface temperature disclosed in related document 1 includes: a meteorological data acquisition step of acquiring meteorological data including at least one of an atmospheric profile at at least one land surface temperature calculation point observed by a meteorological satellite, a satellite zenith angle, emission rate, an emission rate difference, and land surface temperature lapse rate; a land surface temperature calculation point number determination step of determining whether the satellite zenith angle of the meteorological data falls within a predetermined angle and then determining the number of land surface temperature calculation points within the predetermined angle; an emission rate difference calculation step of setting the initial value of first emission rate obtained by detecting the determined land surface temperature calculation points using a first wavelength and the initial value of the second emission rate detected using a second wavelength different from the first wavelength, and obtaining the initial value of an emission rate difference corresponding to the difference between the first emission rate and the second emission rate difference; a predetermined or less value determination step of obtaining the second emission rate by subtracting the first emission rate value from the emission rate difference and then determining whether the second emission rate is less than a predetermined value; a daytime/nighttime/all-based range setting step of setting daytime/nighttime/all-based ranges based on the land surface temperature lapse rate of the meteorological data if, as a result of the determination, the second emission rate is less than a predetermined value; an increased emission rate difference determination step of adding a first predetermined increase value to the emission rate difference, and then determining whether the increased emission rate difference falls within a first predetermined range; an increased emission rate determination step of adding a second predetermined increase value to the first emission rate, and then determining whether the increased emission rate falls within a second predetermined range; and a simulation data generation step of generating daytime/nighttime/all-based simulation data by simulating the land surface temperature using a radiative transfer model.
However, since the method of calculating land surface temperature disclosed in related document 1 measures temperature via the sensor and performs estimation, the estimated temperature is different from a temperature measured via actual measurement due to atmospheric effects and emissivity. The radiant energy radiated from a land surface is attenuated by the scattering, absorption and refraction of the atmosphere and then collected by the infrared sensor, and the emissivity varies with the color, roughness, water content, etc. of the land surface. Accordingly, it is difficult to know emissivity, and thus it is very difficult to estimate accurate temperature from an infrared image.
According to Korean Patent Application Publication No. 2009-0088131 (hereinafter referred to as “related document 2”), the method for estimating a local air temperature taking account of an elevation difference disclosed in related document 2 includes: a digital map generation step of generating a digital map ArcView Shape of a target area, indicating a plurality of observation points on the digital map, storing actually measured air temperature and elevation data on the observation points; a primary air temperature distribution diagram generation step of generating a primary air temperature distribution diagram by forming a plurality of grids by dividing the digital map by a square grid having a predetermined size and calculating the first estimated air temperature value of each of the grids through the Inverse Distance Squared Weighting (IDSW) of the observation points; an actually measured elevation map generation step of generating an actually measured elevation map of the target area as a digital elevation model; a virtual elevation map generation step of generating a virtual elevation map by calculating the virtual elevation of each of the grids of the digital map through the inverse distance squared weighting (IDSW) of the observation points; a correction value generation step of calculating the elevation difference of each of the grids by comparing the actually measured elevation map with a virtual elevation map and generating a correction value by multiplying air temperature lapse rate corresponding to the elevation difference by the elevation difference; and a final air temperature distribution diagram generation step of generating a final air temperature distribution diagram, in which a second estimated air temperature value approximate to the actually measured air temperature value has been indicated, by applying the correction value to the primary air temperature distribution diagram generated at the correction value generation step.
However, the method and system for estimating a local air temperature taking account of an elevation difference disclosed in related document 2 is disadvantageous in that precision is reduced because the estimated value of a local temperature is corrected by applying the temperature lapse rate corresponding to the elevation difference.